The present invention relates generally to electrical conductor termination modules of a type commonly used in high voltage underground electric power distribution systems to connect the cables and operating components of such a system together. More specifically, the invention relates to means for controlling arc-generated gases developed in such modules when a pair of conductors housed therein are separated to create an arc.
In recent years it has become common practice to utilize plug-on type electric cable termination modules in underground power distribution systems in order to provide a convenient means for connecting and disconnecting the various components of the system. While it is generally recognized as being safe practice to de-energize any portion of an underground power distribution system in which a circuit component is to be disconnected from the system, prior to such a disconnection being effected, this practice is not always followed. In fact, due to the difficulty in ascertaining with certainty when such an electric power distribution system is energized, a pair of cable termination modules may be inadvertently disconnected when a system is energized, although the lineman making the disconnection might think the system had been previously de-energized. Also, on relatively low voltage power distribution systems, with modern loadbreak conductor termination modules, it is possible that some experienced lineman may consciously open, or disconnect, an energized circuit, relying on the arc-quenching capability of the load-break termination to extinguish any resulting arc.
Prior to the present invention, it was recognized that ionized gases generated by an arc during the separation of a pair of energized conductors, mounted respectively in a mated pair of conductor termination modules, could cause a possible re-strike of an arc after the initial arc had been extinguished by an arc-snuffing mechanism within the loadbreak modules. Various devices have been developed to deal with such arc-generated gases to reduce the risk of a re-strike arc, or the formation of an arc from one of the energized conductors to ground. One example of such a prior art device is the gas shield and flow directing means disclosed in U.S. Pat. No. 3,587,035--Kotski, entitled "Gas Shield for Load-Break Cable Termination", which issued June 22, 1971 and is assigned to General Electric Company.
The type of gas flow controlling shield disclosed in the above-mentioned Kotski patent has proven to be successful in adequately containing hot ionized gases when used on cable termination modules for electric power distribution systems in the 15 KV range. However, it has been found that on higher voltage power distribution systems, such as those having a rating of 25 KV, it is desirable to provide supplementary means for preventing the escape of most arc-generated gases from loadbreak termination modules during a loadbreak operation. By thus containing the ionized gases within a loadbreak cable termination module, the normal high dielectric strength of air surrounding a pair of separated loadbreak modules is not impaired, so even relatively high line voltages do not usually cause an arc re-strike, or an arc to ground.
One prior art approach to this problem of controlling arc-generated, ionized gases within a loadbreak cable termination module was to provide a gas expansion chamber within the module, into which such gases could be vented during a loadbreak operation. In fact, such auxiliary venting chambers have been provided with pressure responsive valves to further control the flow of gases within the module. An example of such a prior art gas flow control mechanism within an electric power cable termination module is shown in U.S. Pat. No. 3,539,972--Ruete et al., entitled "Electrical Connector for High Voltage Electrical Systems", which issued Nov. 10, 1970 and is assigned to Amerace-ESNA Corporation. One disadvantage inherent in such prior art gas flow control mechanisms is that they do not provide a means for sealing the outermost end of the module to prevent ionized gases from escaping past it into the air surrounding the module. Accordingly, it is possible for a substantial volume of ionized gas to escape from such a loadbreak module when a separable conductor is withdrawn from the module. The ionized gases simply follow the path of the separable conductor out of the loadbreak module.
After recognizing the foregoing disadvantage of the pressure-responsive valve, auxiliary gas expansion chamber type of cable termination modules, an improved type of gas-trap valve was developed for high voltage conductor termination modules. This improved gas-trap valve mechanism was designed to retain substantially all of the arc-generated gases within a loadbreak termination module following a loadbreaking operation. One form of this improved type of gas-trap valve is disclosed in co-pending U.S. Pat. application No. 160,798 filed on July 8, 1971 (General Electric Company which was mailed to the U.S. Patent Office on July 7, 1971), entitled "Electric Cable Termination Module Having a Gas-Trap Valve". That application is assigned to General Electric Co. The gas-trap valve mechanism disclosed in that co-pending application is also described in detail below, since the present invention is ideally suited for use in combination with such a gas-trap valve.
It has been found that the arc-generated gases developed by loadbreak operations in cable termination modules designed for use on 25 KV systems develops extremely high gas pressures very rapidly. These high gas pressures, coupled with the presence of the relatively high voltages on such systems, make it difficult to insure against possible arc restrikes, or arcs to ground, when a pair of cable termination modules on such a system are opened. This problem is traceable primarily to the fact that it is difficult to manufacture a gas-trap valve that will seal a loadbreak cable termination module rapidly enough, after a separable contact is removed from the module, to prevent the escape of some ionized gas therefrom. This problem is somewhat aggravated by the common practice of providing an arc-snuffing rod or arc follower on the separable contact of conventional cable termination modules that are adapted to cooperate with a loadbreak termination module to afford a loadbreak function. Since, during a normal loadbreak operation within such a termination module, an arc is drawn along the surface of such an arc follower for an appreciable interval of time before the arc follower is sufficiently withdrawn from the loadbreak module to enable a gas trap valve to be closed thereby sealing the module, it is possible for ionized gas to escape past the valve during this interval. In addition, even after the separable contact and its arc follower are completely withdrawn from the loadbreak module so that the gas trap valve is free to close, the moment of inertia of such valves causes an inherent time delay during which additional ionized gases can escape past the valve.
Accordingly, it is a primary object of the present invention to provide an improved gas flow restricting means for a high voltage cable termination module in order to substantially reduce the escape of ionized, arc-generated gases from the module during, and following, a loadbreak operation within the module.
Another object of the invention is to provide a gas flow restricting valve means for a loadbreak cable termination module which is operable to cool ionized gases, thereby to increase the dielectric strength of such gases prior to their emission from the module.
Yet another object of the invention is to provide a low-friction gas restricting valve means for a pair of separable connectors of the rod-and-bore type, in order to prevent the escape of ionized, arc-generated gases between the rod and bore contacts during and following an arc-interrupting separation thereof.
Additional objects and advantages of the invention will become apparent to those skilled in the art from the description of it that is given herein, taken in conjunction with the accompanying drawings.